Stimulated secretion of pituitary hormones in normal humans: a novel direct assessment from blood concentrations.

Abstract

Gland responsiveness is usually assessed by administering suitable secretagogues and measuring the resulting hormone concentration in blood after the specific stimulus. Such response-to-stimulus tests are routinely conducted for the clinical diagnosis of pathologies involving the pituitary hormones growth hormone, prolactin, luteinizing hormone, follicle stimulating hormone, adrenocorticotropic hormone, and thyrotropin hormone. However, the current evaluation approaches, based on the maximum peak value or the (normalized) area under the curve, are inadequate under several respects. A more physiologically based index of responsiveness is the amount of released hormone. This is not directly accessible but is typically estimated by (computationally expensive) deconvolution analysis. The present work derives a simple formula yielding the amount of released hormone as a linear combination of blood concentrations through proper weights depending on hormone kinetics and sampling protocol. The weights are derived and reported for all six pituitary hormones and the more common sampling protocols. A validation study involving 174 test experiments has been carried out. The use of the formula shows excellent agreement with the cumulative secretion estimates obtained through deconvolution analysis.